Field of the Invention
The present invention relates to radio communication, and more particularly, to a method of cancelling a self-interference (SI) signal at a radio frequency (RF)-front end and a user equipment (UE) for the same.
Discussion of the Related Art
A full-duplex radio (FDR) or full-duplex communication scheme refers to a communication scheme for simultaneously supporting transmission and reception using the same resource in one user equipment (UE). In this case, the same resource refers to the same time and the same frequency. FDR communication or full-duplex communication is referred to as two-way communication.
FIG. 1 is a diagram illustrating concept of a UE and a base station (BS), which support FDR. Referring to FIG. 1, in a network state that supports FDR, there are three types of interferences. First interference is intra-device self-interference. The intra-device self-interference refers to interference caused by signals that are transmitted from a transmission (Tx) antenna and received by a receiving (Rx) antenna in one BS or UE. Since the signals transmitted from the Tx antenna are transmitted with high power and a distance between the Tx antenna and the Rx antenna is small, the transmitted signals are received by the Rx antenna while attenuation is barely caused, and thus, are received with higher power than a desired signal. Second interference is UE to UE inter-link interference. In a network that supports FDR, the UE to UE inter-link interference is increasingly caused. The UE to UE inter-link interference refers to interference caused by uplink signals that are transmitted from a UE and received by an adjacently positioned UE. Third interference is BS to BS inter-link interference. Similarly, in a network state that supports FDR, BS to BS inter-link interference is increasingly caused. The BS to BS inter-link interference refers to interference caused by signals that are transmitted between BSs or heterogeneous BSs (pico, femto, and relay) in a HetNet state and received by an Rx antenna of another BS.
Among the three types of interferences, the intra-device self-interference (hereinafter, referred to as self-interference) is influence of interference caused only in FDR. In order to manage FDR, a most serious problem is cancellation of self-interference. However, methods for effectively cancelling self-interference in an FDR state have not been discussed in detail.